1. Field of the Invention
This invention relates to an intermediate transfer medium provided with an image-receiving adhesive layer on which an image pattern is formed by a sublimation transfer means in accordance with image data and which is used to produce an image-recorded article such as an identity card (hereinafter "ID card") by transferring the image-receiving adhesive layer to a transfer substrate such as a card material. This invention also relates to a process for producing the image-recorded article.
2. Description of the Prior Art
As known in the art, a process for producing an image-recorded article by forming on an image-receiving adhesive layer of an intermediate transfer medium an image pattern by a sublimation transfer means in accordance with image data and transferring the image-receiving adhesive layer of the intermediate transfer medium to a transfer substrate by thermal transfer has been available (see Japanese Patent Application Laid-open No. 63-81093).
This conventional process will be detailed below. The intermediate transfer medium used in this process is basically comprised of an any desired heat-resistant base sheet and provided on one side thereof at least an image-receiving adhesive layer formed of a thermoplastic resin capable of being dyed with a sublimation (or thermal conversion) dye.
A heat-sublimation ink layer of a transfer ribbon, containing a coloring material comprising a sublimation dye, is brought into contact with the image-receiving adhesive layer of such an intermediate transfer medium, and a thermal head is brought into pressure contact with it from the side of the transfer ribbon, where electrical signals Generated in accordance with image data are applied to the thermal head with heating to cause the dye in the heat-sublimation ink layer to imagewise transfer to the image-receiving adhesive layer to form an image pattern on that layer. In the case when the image data represent multiple colors, transfer ribbons with different colors are applied and a like process is repeated necessary times to form a multi-color image pattern on the image-receiving adhesive layer of the intermediate transfer medium.
Next, the intermediate transfer medium on which the image pattern has been formed through the above process is brought into contact with the surface of a transfer substrate, and a heating medium such as a heat roll or a heat plate is pressed against it from the side of the intermediate transfer medium to carry out heating so that at least the image-receiving adhesive layer of the intermediate transfer medium is thermally transferred to the transfer substrate. Thus, an image-recorded article such as an ID card is produced. Here, the image-receiving adhesive layer is comprised of a thermoplastic resin and serves also as an adhesive.
This process has the advantages that the image pattern is formed of a sublimation dye and can be sharp, and the image can be formed without any particular limitations on the type of the transfer substrate.
However, in carrying out the above process, it comes into question what material should be selected for the image-receiving adhesive layer in the intermediate transfer medium. More specifically, in the step of forming the image pattern the layer is heated while it is in contact with the transfer ribbon, and hence there is a possibility that the image-receiving adhesive layer is transferred or thermally melt-adheres to the transfer ribbon side when the thermoplastic resin constituting the image-receiving adhesive layer has a low heat-melting temperature. In order to prevent this unauthorized transfer, one may contemplate to use in the image-receiving adhesive layer a thermoplastic resin having a higher heat-melting temperature. This, however, makes it necessary to raise the temperature of the heating medium in the step of transferring the image-receiving adhesive layer to the transfer substrate, so that the image pattern comprised of a dye may deteriorate or fade and also a damage due to heat may be caused in the transfer substrate. Meanwhile, in order to decrease the adhesion to the transfer ribbon, one may also contemplate to mix an additive such as silicon in the image-receiving adhesive layer. In such a case, however, a problem may arise such that the adhesion to the transfer substrate becomes poor.
The image-recorded article produced by this process has an image pattern and accordingly can be used in ID cards such as membership cards. Since, however, no attention has been paid to the prevention of forgery or falsification of the image pattern, and there is the problem that the image pattern tends to be forged or falsified.